The amendment to the lawsuit comes as a federal grand jury in Pennsylvania weighs evidence to determine whether Wal-Mart will face criminal charges in the use of illegal immigrants to clean its stores.

A lawyer for Wal-Mart denied the new allegation.

INS agents raided Wal-Mart stores across the country on Oct. 23 in a sweep that resulted in the arrest of hundreds of janitors on immigration charges.

Among those arrested were the 17 named plaintiffs in the civil suit, including 11 Mexican immigrants who were the original plaintiffs, plus six Eastern Europeans added to the list Monday. The lawsuit seeks class-action status for perhaps thousands of immigrants.

The suit claims some workers were forced to work seven-day, 70-hour weeks for $1,500 a month. The amended claim follows a report in The New York Times that contained the separate allegation that janitors were being locked in.

The lawsuit is being brought under the federal Racketeer Influenced Corrupt Organizations Act, charging that Wal-Mart systematically violated workers’ rights and tried to shield itself from liability by using independent contractors to employ the immigrants.

David Murray, a lawyer for Wal-Mart, said the allegations were “absolutely incorrect.”

Murray said concern for workers’ rights was the reason the chain eliminated the use of cleaning contractors in 80 percent of its stores. Wal-Mart has 3,500 stores nationwide with 1.2 million employees.

Murray acknowledged that doors were kept locked, but insisted that a manager with a key was always present.

“This was simply an effort to keep the employees safe and keep the merchandize secure,” Murray said.